I would be very suprised if the 247 gr AT needed more then a 1-8 twist. When Richard was playing with them, he made me some 290 gr ULD RBBT prototypes that were even a bit longer then the listed 247 gr by a few thou.
He wanted me to test them in my 1-8 twist 300 AX and I was more then happy to. The problem was not stability, it was integrity. At the velocity I was able to drive them to, about 75% of them came apart. I learned that the hard way, lost one muzzle brake
and a chrono graph in that testing!!!
I was driving them to around 3100 fps and I would get as I mentioned, 1 out of 4 to land on target. Those that did were very accurate and obviously fully stabilized as I tested them out to a mile and the bullets that actually made it to the target were extremely consistant.
The problem when you get a bullet this long you need a relatively fast twist rate but there is a fine line between over spinning and keeping them stable. I am not talking about over stabilization, I am talking about the bullets being able to survive the launch speeds or should I say RPMs.
I am hoping and praying Paul can get these 30 cals figured out. My 300 AX is screaming for a good high BC bullet. If we could get one that would take the velocity, my 300 AX may be the best of the bunch between the 7mm AM, 300 AX and 338 AX.
Next step would be for him to figure a way to get them to survive a 3500 fps launch speed, I have a 300 Allen Magnum reamer sitting here that has never been used!!! Yep, that one is based on the 408 CT!!!
I was able to down load the 290 gr prototypes to where around 50% were surviving the launch but could do no better. I then tested them in a 1-8 twist 300 RUM to see if I could get them down in speed a bit more to see if they would survive and never could get consistant performance.
It all depends on the jackets, it was the problem back then and it still is, I hope Paul can get them figured out, I would love to have the AMs and AXs spitting wildcat bullets again. They are most impressive anyway but they become really special with the bullets they were designed around.
Take care old friend!!!!